There is known a wire cut electrical discharge machining apparatus which includes a device for feeding an electrode wire automatically through the material to be machined.
FIG. 1 is a schematic illustration of the conventional apparatus in its operating position. An electrode wire 10 is supplied from a wire supply reel not shown to the material 12 to be machined. The material 12 has an initial hole 14 through which the wire 10 extends. The material 12 to be machined is moved in the X and Y directions relative to the wire 10 by a driving device not shown. The material 12 is machined during its movement relative to the wire 10. The wire 10 extends through a tubular guide 16 provided at its lower end with a guide die 18 for guiding the electrode wire 10 in the machining area. Another guide die 20 is provided on the top of a lower guide 22 for guiding the wire 10 below the material 12. A plurality of electricity feeders 24 are located in contact with the wire 10 to supply electrical energy for the machining operation from a power source 26 to the wire 10. The tubular guide 16 has a corresponding number of openings 28 in each of which one of the feeders 24 is located. Another electricity feeder 30 is provided in the lower guide 22 for supplying electrical energy from the power source 26 to the wire 10 below the material 12 to be machined. A pair of nozzles 32 and 34 are provided above and below the material 12 for jetting a working fluid 36 into the electrical discharge machining area between the wire 10 and the material 12 to be machined. A bearing 38 is provided in the upper nozzle 32 for supporting the tubular guide 16. Each of the nozzles 32 and 34 has an inlet 40 or 42 for the working fluid 36. A pair of pinch rollers 44 are provided at the top of the tubular guide 16 for feeding the wire 10 to the lower guide 22 through the tubular guide 16. The pinch rollers 44 are driven by a drive motor not shown to move the wire 10 down. The tubular guide 16 is vertically movable along a guide bar 52 by a motor 46, a feed screw 48 and a slider 50. The motor 46, feed screw 48, slider 50 and guide bar 52 define a vertical drive system 80 for the tubular guide 16. The vertical movement of the tubular guide 16 facilitates the insertion of the wire 10 into the lower guide 22. A cutter 54 is provided for cutting the wire 10 after the tubular guide 16 has been raised by the motor 46 to a position above the cutter 54. A pair of rollers 56 are provided for pulling the wire 10 down through the lower guide 22. The wire 10 is fed out of the apparatus by a pair of rollers 60 provided with a belt 58, and a motor 62 connected to the rollers 60.
FIG. 2 shows the position of the apparatus shown in FIG. 1 in which the electrode wire 10 is fed to the lower guide 22. The tubular guide 16 is lowered by the drive motor 46 to the lower guide 22 through the initial hole 14 of the material 12 to be machined. The electricity feeders 24 are moved away in the directions of arrows in FIG. 2 by a drive unit not shown in order to enable the downward movement of the tubular guide 16.
FIG. 3 shows the position of the apparatus shown in FIG. 1 in which the wire 10 is cut. The tubular guide 16 is raised by the vertical drive system 80 to a position above the cutter 54, and the cutter 54 is moved in the directions of arrows in FIG. 3 by a drive unit not shown to cut the wire 10. The cutting of the wire 10 also requires the movement of the feeders 24 away from the tubular guide 16 as shown by arrows.
The wire cut electrical discharge machining apparatus constructed as shown in FIG. 1, and adapted for operation as hereinabove described with reference to FIGS. 2 and 3 has a number of disadvantages. It is necessary to move the electricity feeders 24 away from each other to enable the vertical movement of the tubular guide 16, and toward each other to supply electricity to the wire 10 when the material 12 to be machined is machined. A separate mechanism is required for moving the feeders 24, and fine control is required for bringing the feeders 24 into proper contact with the wire 10. The strength of the tubular guide 16 is reduced by the presence of the openings 28 provided for enabling the supply of electricity from the exterior of the guide 16 to the wire 10. When the apparatus is set for the machining operation, it is impossible to move the tubular guide 16 vertically to its optimum position suited for any possible variation in the thickness of the material 12 to be machined, since the feeders 24 are not vertically movable.